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View Full Version : Turning the bleeds off during a GPWS escape manoeuvre


BmPilot21
26th May 2002, 22:00
What if one of us (god forbid) found ourselves having to perform a GPWS escape manoeuvre for real, and having set full thrust, pitching to the stick shaker, and retracting the speedbrake a/r (ref. the Cali accident), found that ground contact was still imminent?

If you've got the presence of mind, and once you've fire-walled the thrust levers, why not turn off the engine bleeds, along with the engine anti-ice? It often seems that CFIT accidents involve the aircraft hitting a ridge maybe only a few feet below the summit, and turning the bleeds off might just save your life. Obviously a job for PNF, once you've done the important stuff like making sure full thrust is set, speedbrake retracted, and exercising your bowels!

411A
26th May 2002, 22:20
BmPilot21...
If you are a young guy (suspect so)...then hats off to you. THINKING pilots (as opposed to..."just read the check list Sid, never mind the brain)...are really needed...when the chips are down. When the situation dictates....everything MUST be used.
CRM is needed here....instead of the nonsense parlor games usually in practice with these courses.

Hand Solo
26th May 2002, 23:09
Given the proximity to terrain required to activate a GPWS warning time is of the essence in responding. By the time you've got TOGA, flown right up to the limit of the stick shaker, rolled wings level and stowed the spoilers I suspect the outcome of the event is already decided. I suppose it could work, but by the time you've looked up, identified the 2/3/4 bleed switches and waited for the valves to close the event is likely to be over one way or another.:eek:

411A
27th May 2002, 00:09
Yes, quite true...but the new EGPWS is a different animal....and is a swell piece of equipment. It will certainly save someone's bacon...where GPWS may not.

West Coast
27th May 2002, 05:12
I fly in the mountains of the western US. While I have not encountered a GPWS situation, it is somewhat common to fly decreasing performance windshear escape manuevers. For that reason I start the APU and transfer the bleeds to it. Every little bit helps. I have decieded that if ground contact is imminent, I am going to turn off the engine speed switches. Again, every bit of power helps

QAVION
27th May 2002, 08:12
Before you consider doing this on any airplane, I'd make a list of all the the things on your airplane which uses bleed air... E.g. LE flaps, hydraulic pumps, anti-ice, packs, TAT probes, etc...

Note here that some aircraft push out the leading edge flaps/slats automatically if a stall is approached... If these particular leading edge devices are bleed air driven, stopping them operating may or may not help you in your situation (you'd have to consult the people who designed the airplane for help with this).

Rgds.
Q.

Young Paul
27th May 2002, 15:06
"Fly in the mountains"? A cave pilot, maybe? :)

Sorry. Undergraduate sense of humour, plus a bit of pedantry ...

Also, I'd be highly surprised if a critical safety item like bleed activated slats/flaps would be disabled by switching off engine bleeds.

tinyrice
27th May 2002, 15:41
Carefull now! A lot of the bleed and anti-ice valves and stuff that you want to work for you, are electrically actuated, air operated. You may be making it harder for the aeroplane to do what you expect.

foxtrot
27th May 2002, 22:27
hye BmPilot21
though i agree with 411A but going for the bleeds at a time like GPWS escape manoeuvre i dont think so. do not distract your self or the other guy, when the GPWS goes of you will enough to do believe me,bye the time you go for the bleeds it is over either ways. keep thinking .
see ya

Right Way Up
28th May 2002, 19:06
On my aircraft the bleed switches look like AC Bus switches which in a rush could make your problem a lot worse!